Egodriver Problem

[gtr2]

I don't know exactly what the voltages are but these seem about right.  Pin 4 is the ground pin so it should register around 0

You need your audio probe to pin point where you're having the issue.

Josh

[jkokura]

Everything to me is pointing to either a bad IC, a bad diode, or a bad pot. Because it's only your gain pot that's doing this, it has to be in the parts between the pot and the IC, so C2 and C3, and R4 and R5, and the pot and IC of course.

Have you tried a new pot? Have you tried a new IC?

Jacob

[tenwatt]

Everything to me is pointing to either a bad IC, a bad diode, or a bad pot. Because it's only your gain pot that's doing this, it has to be in the parts between the pot and the IC, so C2 and C3, and R4 and R5, and the pot and IC of course.

Have you tried a new pot? Have you tried a new IC?

Jacob

I built my probe and tested everything.  The pot seemed fine.  I got signal on each side of C2, C3, and R5.  On R4, on the other hand, there was only signal on one side.  Is that the culprit?

[jkokura]

No R4 goes to ground. That's how it should work.

Bad pot, or IC is still what I'm thinking. Have you got a spare dual op amp?

Jacob

[tenwatt]

I probed the IC and pin #4 gave no signal (ground right?) also pin #8 gave a VERY weak signal.

[jkokura]

Pin four is ground, and pin 8 is 9V in. Threre souls be sound on the power rail.

It's good that you're probing, but do you have another IC to try? That may be the problem.

Jacob

[tenwatt]

Pin four is ground, and pin 8 is 9V in. Threre souls be sound on the power rail.

It's good that you're probing, but do you have another IC to try? That may be the problem.

Jacob

The only other IC I have right now is a LM1458.

Just to be sure I put the meter on the 1 and 3 lugs of the pot.  It measured .894M from 0 to 10.  I put it on the 1 and 2 lugs and it was at 1.2 ohm at 0 and .891M at 10.  The pot's good right?  I detached it from the board.

EDIT:  I found a TLC2272 and put it in there and it continued to do the same thing.

[tenwatt]

The only other IC I have right now is a LM1458.

Just to be sure I put the meter on the 1 and 3 lugs of the pot.  It measured .894M from 0 to 10.  I put it on the 1 and 2 lugs and it was at 1.2 ohm at 0 and .891M at 10.  The pot's good right?  I detached it from the board.

EDIT:  I found a TLC2272 and put it in there and it continued to do the same thing.

So are those readings good on the pot?  If so...what should I check next?

[jkokura]

Hey man, sorry I didn't get back.

Yes, it sounds like your Pot is fine.

I'm perplexed. I've never heard this phenomenon, nor have I any idea what the problem could be considering everything I would expect it to be checks out to be fine.

Here's what I propose you do now. Make the circuit do the strange noise by turning the gain pot up. Use your audio probe to trace backwards through the circuit from the output. When you get no strange noise, work forward until you do get strange noise. Whatever part is in between is where your problem is.

Keep your schematic handy, and cross parts off the list that don't seem to be the problem. If it's not in the gain structure element of the pot, it's got to be somewhere afterwards. Because the trannies and diode clipping seems to be fine also, it's probably after that also. If this is still acting up, you might need to take a break from it, because sometimes you just need to walk away for a bit.

Jacob

[tenwatt]

Thanx for the feedback.  I'll be on it as soon as I get home.  Go figure...my very first build results in an unknown phenom. 

I really am grateful for everyone's time and help.

[tenwatt]

Okay, I started probing on the "In" of the board. 

R1 was good on one side, ground on the other.
C1 was good on both sides.
R2 was good on both sides.
R3 was good on one side....but the other side produced the stutter.

Did I find the problem? 

[jkokura]

Obviously it's a part of the problem, but which side of R3? One side connects to the ic input, and the other to VB, so which side?

Jacob

[tenwatt]

Obviously it's a part of the problem, but which side of R3? One side connects to the ic input, and the other to VB, so which side?

Jacob

I believe it's the pad connected to VB.  If you're looking at the board it's the bottom lug just above the ground.

[jkokura]

Yeah, that's the one. That means that the problem could be with your power supply, or with any of the parts connected to your power rail. Have you checked your power supply yet? What your ground? If you power is leaking to ground in a very small amount I would bet that would cause some crazy symptoms...

What I don't get is why it only happens when you turn up your gain pot!

Jacob

[tenwatt]

Yeah, that's the one. That means that the problem could be with your power supply, or with any of the parts connected to your power rail. Have you checked your power supply yet? What your ground? If you power is leaking to ground in a very small amount I would bet that would cause some crazy symptoms...

What I don't get is why it only happens when you turn up your gain pot!

Jacob

The ground reads 0mV and the "9V" reads 9.25V.  What's the "power rail"?